Effect of Varying Chalcogenophene Spacer Between Indole and Benzothiadiazole Based D-A-D type Semiconducting Small Molecules on the Organic Field Effect Transistors (OFETs) Characteristics

Abstract

Introducing selenophene and furan analogs as alternatives to widely used thiophene derivatives has garnered significant interest in semiconductors for enhancing optoelectronic properties and performance in electronic applications.1-5 In this study, we report the synthesis of two novel donor-acceptor-donor-based small molecules: diethyl 6,6'-(benzo[c][1,2,5]thiadiazole-4,7-diylbis(furan-5,2-diyl))bis(1-dodecyl-1H-indole-2-carboxylate) [IN-BT2F-IN] and diethyl 6,6'-(benzo[c][1,2,5]thiadiazole-4,7-diylbis(selenophene-5,2-diyl))bis(1-dodecyl-1H-indole-2-carboxylate) [IN-BT2Se-IN]. These molecules incorporate furan and selenophene spacers, respectively, bridged between indole (IN) and benzo[c][1,2,5]thiadiazole (BT) units and were investigated for their potential applications in Organic Field-Effect Transistors (OFETs). The selenophene-based material exhibited an average hole mobility of 0.019 cm² V⁻¹ s⁻¹, with a maximum of 0.025 cm² V⁻¹ s⁻¹ under annealing conditions, whereas the furan analog was OFET-inactive even after thermal annealing. We also evaluated the previously reported thiophene analog (IN-BT2T-IN) alongside these newly synthesized molecules for a systematic comparison. The findings demonstrate that OFET properties can be modulated by altering the spacer molecules within the same donor-acceptor framework. Specifically, replacing the thiophene spacer with selenophene between indole and benzothiadiazole led to a drastic improvement in hole mobility by one order of magnitude.